Process for producing filament and filament assembly composed of thermotropic liquid crystal polymer

ABSTRACT

A process for producing a filament assembly composed of a thermotropic liquid crystal polymer, which comprises melt extruding a thermotropic liquid crystal polymer through an orifice nozzle into a high-speed fluid to thereby hold filaments spun right under the spinning nozzle at a high temperature, so that the filaments are taken up at a high draft ratio by the frictional force of the high-speed fluid.

This application is a division of Ser. No. 08/433,313, May 3, 1995, U.S.Pat. No. 6,051,175.

TECHNICAL FIELD

The present invention relates to processes for producing aheat-resistant filament and filament assembly of high strength and highelastic modulus each composed of a thermotropic liquid crystal polymer.Further, the invention relates to processes for producing a filament anda filament assembly in which a thermotropic liquid crystal polymer ismixed with another extrudable polymer and to the above filamentassembly.

BACKGROUND ART

Since the emergence of a thermotropic liquid crystal polymer, the heatresistance thereof and the attainability of high strength and highelastic modulus thereby have been noted and thus some prior arts havebeen developed with respect to the process for producing the fiber (see,for example, U.S. Pat. Nos. 3,975,487, 4,468,364 and 4,161,470 andJapanese Patent Laid-Open Gazette No. 196716/1988).

It is known that the thermotropic liquid crystal polymer can have highstrength and high elastic modulus only by spinning if it Is performedunder appropriate conditions. Further, it is known that the heattreatment and redrawing can improve the strength and elastic modulusthereof. In particular, it is reported that some types exhibit astrength improvement to 5 to 6 times the original.

In the spinning of the above conventional thermotropic liquid crystalpolymer filament, it has been necessary to conduct the spinning with theuse of a nozzle having a very minute aperture for obtaining a finedenier filament because it is difficult to increase the draft ratiothereof. Further, extrusion abnormalities such as melt fracture arelikely to occur. Thus, the extrusion rate cannot be made high resultingin extremely poor productivity.

Therefore, with respect to the properties of the obtained filament, noprocesses have been established for stably producing a filament with theultimately high strength and elastic modulus at high productivity excepton a laboratory scale.

The inventors have conducted extensive investigations into the causes ofthe low productivity of the prior art, the difficulty in stablyproducing a product with high strength and high elastic modulus and thepoor spinning operation efficiency (end breakage, denier nonuniformityand product quality dispersion, etc.) in connection with the meltspinning of the thermotropic liquid crystal polymer filament. As aresult, the following has been found.

(1) The thermotropic liquid crystal polymer as a starting material isnot always uniform.

The cause is in an aspect an inevitable consequence of the technology ofpolymerizing the thermotropic liquid crystal polymer. In other aspects,the cause relates to the heat history difference and heat deteriorationafter polymerization and the increase of polymerization degree by heattreatment. With respect to these, a rapid product quality improvementhas been attained for the recent years by virtue of, for example,polymerization and subsequent treatment technologies andpost-polymerization filter technologies. However, the improvement isstill not satisfactory.

(2) The melting point of the thermotropic liquid crystal polymer is sohigh that, after leaving the spinning nozzle, the surface of thefilament is cooled by the temperature of the atmosphere with the resultthat the draft ratio cannot be made high.

Thus, a skin layer is formed at the surface of the filament, therebycreating a structural difference between the inner part and the surfacepart. This is an obstacle of the high quality (for example, highstrength, elastic modulus and elongation). In the spinning of thecustomary thermoplastic polymers, the draft ratio can be increased inthe form of a melt having left the nozzle to thereby orient themolecules. However, with respect to the thermotropic liquid crystalpolymer, greater belief is in that the orientation is completed in thenozzle, and the thought has not arrived at a concept of stablyincreasing the draft ratio upon leaving the nozzle.

(3) The nozzle diameter is reduced for increasing the orientation in thenozzle. Further, the reduction of the nozzle diameter is inevitable forobtaining a fine denier because the above draft ratio cannot beincreased.

However, the extrusion rate is proportional to fourth power of thenozzle diameter, so that the reduction of the nozzle diameter leads toextremely poor productivity. Further, the shear rate of the extrusion isinversely proportional to third power of the nozzle diameter, so thatthe reduction of the nozzle diameter leads to extremely high shear rate,thereby causing extrusion abnormalities such as melt fracture. With theuse of a polymer having instability factors in its starting materialsuch as the thermotropic liquid crystal polymer, stable operation cannotbe conducted at shear rates close to the extremity.

(4) The thermotropic liquid crystal polymer filament is a functionalfiber with high strength, elastic modulus, chemical resistance and heatresistance and further excellent electrical properties. However, it isalso an industrial fiber, so that how cheaply the thermotropic liquidcrystal polymer can be produced is important.

However, because of the above factors (1) to (4) affecting incombination, it has been unfeasible to stably produce a fine denierfilament of thermotropic liquid crystal polymer with high strength andhigh elastic modulus on an industrial scale.

Often, the thermotropic liquid crystal polymer filament is used as anindustrial reinforcing fiber in FRP, FRTP, concrete reinforcement andthe like. In such uses, the thermotropic liquid crystal polymer mustexhibit improved affinity for, adhesion to and uniform miscibility withthe matrix.

The above thermotropic liquid crystal polymer has only been formed intofibers but not into a nonwoven web or a filament assembly becausespecial spinning means and subsequent heat treatment are requiredtherefor. In a simple assembly of rigid thermotropic liquid crystalpolymer filaments, the filaments cannot be mutually entangled, so thatthe assembly is readily disintegrated with external force, therebydisenabling the holding of the outline as a filament assembly. Althoughthe fixing with an adhesive can be thought of, the use of the adhesiveis unfavorable because it generally degrades the heat resistance andelectrical properties of the filament assembly. Further, heat-resistantadhesives are expensive.

A technique comprising shortly cutting the conventionally producedthermotropic liquid crystal polymer filament to thereby form the sameinto a nonwoven web or a paper has been reported (EPC Patent Laid-OpenGazette No. 167682 (A)). However, not only is the reinforcing effect ofshort fibers poor in the use in FRP and FRTP but also additional stepssuch as adhesive bonding and fibrillation for formation into a nonwovenweb or a paper are inevitable. The fibrillation has a drawback ofdegrading the performance of the highly elastic fiber.

The heretofore proposed processes for producing a filament assembly or anonwoven web from the thermotropic liquid crystal polymer filaments havedrawbacks in that not only is a cost increase inevitable but also theproduction of a nonwoven web or filament assembly of long-fiberfilaments is difficult and the quality of the resultant product is poor.Specifically, there are problems such that a binder is requisite foruniformity and filament integration and that the filaments are notloosened.

A filament of high strength and high elastic modulus cannot be obtainedby melt spinning the thermotropic liquid crystal polymer through themelt spinning nozzle conventionally employed in the filament spinningfollowed by free fill and flow. Instead, the filament diameter isunfavorably large and an impracticable filament assembly (nonwoven web)results.

The reason has been revealed to be that the filament having exited thenozzle is oriented by the nozzle shear rate to thereby have increasedstrength and further the surface of the filament is cooled to solidifybecause of high melting point, so that only the weight thereof does notlead to application of a draft with the result that the filamentdiameter cannot be decreased.

An extreme increase In the shear rate in the nozzle for increasing themolecular orientation results in extrusion abnormalities such as meltfracture in the nozzle, end breakage upon exiting the nozzle and blockformation (bundling) at the corresponding part in a filament assembly.Thus, a filament assembly of high quality cannot be obtained.Especially, in the filament assembly from the thermotropic liquidcrystal polymer, uniform polymer cannot be obtained in thepolymerization of the thermotropic liquid crystal polymer as a startingmaterial and, further, thermal polymerization or decomposition isadvanced by the influence of heat in the extruder and other means, sothat the polymer dispersion is extensive in that some parts of thepolymer have extremely high molecular weights or rather in the form ofgels while some other parts are decomposed to exhibit low molecularcharacteristics. Thus, extrusion abnormalities are likely to occur.

Therefore, the current situation has been that a filament of highstrength and high elastic modulus cannot be realized in industriallystable conditions.

Moreover, the filaments must be well entangled for forming a filamentassembly. A simple assembly of thermotropic liquid crystal polymerfilaments which are composed of rigid molecular chains and also thick isreadily disintegrated and cannot function as an assembly.

On the other hand, in the use of an assembly of long-fiber filaments ofhigh strength and high elastic modulus in FRP or FRTP, the attainment ofuniform mixing of the filaments with a matrix polymer from not only themicroscopic but also macroscopic viewpoints encounters an extremedifficulty in practice. Parts where the amount of the reinforcingmaterial is small naturally have less reinforcing effect to therebycause product defects, while, at parts where the amount of thereinforcing material is too large, not only is this wasteful but alsothe amount of the matrix resin is unsatisfactory to thereby alsooccasionally cause defects.

Therefore, in the use of continuous long-fiber filaments as reinforcingfibers in, for example, FRP or FRTP, how uniformly the filaments aremixed with the matrix resin is an important task.

In the above use, it is also important to provide the thermotropicliquid crystal polymer filaments as reinforcing fibers with the affinityfor and the adherence to the matrix resin.

In the conventional FRP and FRTP, the arrangement of filaments is randomin the filament assembly. In particular, when a plane strength is to berealized by arranging the filaments in a plane form, the currentsituation is that the filaments are incorporated in the FRP and FRTP inthe form of a prepreg or a woven fabric of the reinforcing filaments. Inthe form of a prepreg or a woven fabric, however, not only are these perse expensive but also the fibers must be used in an excess amountbecause of a dense structure and, further, multiple layers must beincorporated in the reinforcement of a thick object, so thatoccasionally a shaped article as a whole becomes too expensive to put topractical use. Moreover, the prepreg and woven fabric may not fit adelicate configuration of a shaped article.

Therefore, a filament assembly is desired which is cheap and soft buthas the filaments arranged along an intended direction.

Naturally, how effectively the cost reduction can be achieved is animportant task because the thermotropic liquid crystal polymer filamentsare mostly used as industrial materials.

U.S. Pat. No. 4,362,777 discloses a nonwoven web of thermotropic liquidcrystal polymer filaments. However, the filaments are not entangledbecause those right under the spinning nozzle are not in ahigh-temperature atmosphere.

U.S. Pat. Nos. 4,442,266, 4,522,884 and 4,442,057 disclose filamentsobtained by spinning of a blend of a thermotropic liquid crystal polymerand, for example, polypropylene. However, the filaments are notentangled because those right under the spinning nozzle are not in ahigh-temperature atmosphere.

DISCLOSURE OF THE INVENTION

It is a first object of the present invention to provide process forproducing a thermotropic liquid crystal polymer filament of highstrength and high elastic modulus which can stably be produced and whichis improved in the affinity for, adherence to and uniform miscibilitywith a matrix.

It is a second object of the present invention to provide an assemblycomposed of continuous long-fiber filaments by resolving the abovedrawbacks of the prior art, by reducing the cost of the filamentassembly (nonwoven web) while ensuring the heat resistance, highstrength and high elastic modulus of the thermotropic liquid crystalpolymer filament and by improving the affinity for, adherence to anduniform miscibility with a matrix and to provide a process for producingthe same.

The above objects of the present invention can be attained by thefollowing processes for producing a filament and a filament assembly andthe following filament assembly.

That is, the first process of the present invention is defined as aprocess for producing a filament composed of a thermotropic liquidcrystal polymer, which comprises melt spinning a thermotropic liquidcrystal polymer through a spinning nozzle at a draft ratio of at least30 while holding the filament spun right under the spinning nozzle at ahigh temperature (hereinafter referred to as “the process A”).

The second process of the present invention is defined as a process forproducing a filament assembly composed of filaments of a thermotropicliquid crystal polymer, which comprises melt extruding a thermotropicliquid crystal polymer into a high-temperature and high-speed fluidthrough an orifice nozzle to thereby hold filaments spun right under thespinning nozzle at a high temperature, so that the filaments are takenup at a high draft ratio by the frictional force of the high-speed fluid(hereinafter referred to as “the process B”). In this process, the draftratio is increased to thereby not only reduce the filament diameter butalso enhance the degree of molecular orientation so that filaments ofhigh strength and high elastic modulus can be produced.

The third process of the present invention is defined as a process forproducing a filament composed of a thermotropic liquid crystal polymer,which comprises melt spinning a mixture of a thermotropic liquid crystalpolymer and a non-liquid-crystalline polymer through a spinning nozzleat a draft ratio of at least 50 while holding the filament spun rightunder the spinning nozzle at a high temperature (hereinafter referred toas “the process C”).

The fourth process of the present invention is defined as a process forproducing a filament assembly composed of filaments of a mixture of aliquid crystal polymer and another polymer, which comprises meltextruding a thermotropic liquid crystal polymer and anon-liquid-crystalline polymer into a high-speed fluid through anorifice nozzle, so that filaments are taken up at a high draft ratio bythe frictional force of the high-speed fluid and entangled by the fluid(hereinafter referred to as “the process D”). In this process, a highshear rate is realized in the nozzle, so that an assembly of filamentseach having high strength and high elastic modulus can be obtained. Thisprocess ensures uniform mixing and integration of the thermotropicliquid crystal polymer filaments and a matrix polymer in the use of themixed assembly as a reinforcing fiber in FRP or the like.

Moreover, the filament assembly of the present invention comprises aplurality of mutually entangled long-fiber filaments of a thermotropicliquid crystal polymer.

The present invention will be described in greater detail below.

The terminology “thermotropic liquid crystal polymer” used herein meansa thermoplastic polymer which can be melted when being heated andexhibits optical anisotropy when being melted. The above polymer whichexhibits optical anisotropy when being melted has such a property thatthe molecular chains of the polymer take a regular parallel arrangementin the molten state. The characteristics of the optically anisotropicmelt phase can be confirmed according to the customary polarization testmethod in which crossed polarizers are utilized.

Examples of the above liquid crystal polymers include liquid crystallinepolyesters, polycarbonates and polyesterimides. Specifically, (wholly)aromatic polyesters, polyester-amides, polyamide-imides,polyester-carbonates and polyazomethines are mentioned.

The thermotropic liquid crystal polymer generally has a slender flatmolecular structure in which the rigidity is high along the principalmolecular chain and in which there are a plurality of mutually coaxialor parallel chain extending bonds.

The thermotropic liquid crystal polymer for use in the present inventioncomprehend a polyester composed of a polymer chain of which a part iscomposed of a segment that can form an anisotropic melt phase while theremaining part is composed of a segment that cannot form an isotropicmelt phase. They also comprehend a compound polymer prepared bycompounding plural thermotropic liquid crystal polyesters.

Representative examples of the monomers for use in the formation of thethermotropic liquid crystal polymer are:

(a) at least one member selected from aromatic dicarboxylic acids,

(b) at least one member selected from aromatic hydroxycarboxylic acidcompounds,

(c) at least one member selected from aromatic diol compounds,

(d) at least one member selected from aromatic dithiol (d₁), aromaticthiophenol (d₂) and aromatic thiol carboxylic acid (d₃) compounds, and

(e) at least one member selected from aromatic hydroxyamine and aromaticdiamine compounds.

In the polymerization, the monomers of the groups (a) through (e) abovemay be individually employed. However, in many cases, these are employedin combination, e.g., combinations of groups (a) and (c), groups (a) and(d), groups (a), (b) and (c), groups (a), (b) and (e), or groups (a),(b), (c) and (e).

Examples of the aromatic dicarboxylic acid compounds of the group (a)above are aromatic dicarboxylic acids such as terephthalic acid,4,4′-diphenyldicarboxylic acid, 4,4′-triphenyl-dicarboxylic acid,2,6-naphthalendicarboxylic acid, 1,4-naphthalendicarboxylic acid,2,7-naphthalenedicarboxylic acid, diphenyl ether 4,4′-dicarboxylic acid,diphenoxyethane-4,4′-dicarboxylic acid,diphenoxybutane-4,4′-dicarboxylic acid, diphenylethane-4,4′-dicarboxylicacid, isophthalic acid, diphenyl ether 3,3′-dicarboxylic acid,diphenoxyethane-3,3′-dicarboxylic acid, diphenylethane-3,3′-dicarboxylicacid and 1,6-naphthalenedicarboxylic acid; and products of substitutionof the above aromatic dicarboxylic acids with an alkyl, an alkoxy or ahalogen, such as chloroterephthalic acid, dichloroterephthalic acid,bromoterephthalic acid, methylterephthalic acid, dimethylterephthalicacid, ethylterephthalic acid, methoxyterephthalic acid andethoxyterephthalic acid.

Examples of the aromatic hydroxycarboxylic acid compounds of the group(b) above are aromatic hydroxycarboxylic acids, such as 4-hydroxybenzoicacid, 3-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and6-hydroxy-1-naphthoic acid, and products of substitution of the abovearomatic hydroxycarboxylic acids with an alkyl, an alkoxy or a halogen,such as 3-methyl-4-hydroxy-benzoic acid, 3,5-dimethyl-4-hydroxybenzoicacid, 2,6-dimethyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoicacid, 3,5-dimethoxy-4-hydroxybenzoic acid,6-hydroxy-5-methoxy-2-naphthoic acid, 2-chloro-4-hydroxybenzoic acid,3-chloro-4-hydroxybenzoic acid, 2,3-dichloro-4-hydroxybenzoic acid,3,5-dichloro-4-hydroxybenzoic acid, 2,5-dichloco-4-hydroxybenzoic acid,3-bromo-4-hydroxybenzoic acid, 6-hydroxy-5-chloro-2-naphthoic acid,6-hydroxy-7-chloro-2-naphthoic acid and6-hydroxy-5,7-dichloco-2-naphthoic acid.

Examples of the aromatic diol compounds of the group (c) above arearomatic diols, such as 4,4′-dihydroxydiphenyl, 3,3′-dihydroxydiphenyl,4,4′-dihydroxytriphenyl, hydroquinone, resorcinol, 2,6-naphthalenediol,4,4′-dihydroxydiphenyl ether, bis(4-hydroxyphenoxy)ethane,3,3′-dihydroxydiphenyl ether, 1,6-naphthalenediol,2,2-bis(4-hydroxyphenyl)-propane and bis(4-hydroxyphenyl)methane, andproducts of substitution of the above aromatic diols with an alkyl, analkoxy or a halogen, such as chlorohydroquinone, methylhydroquinone,t-butylhydroquinone, phenylhydroquinone, methoxyhydroquinone,phenoxyhydroquirone, 4-chlororesorcinol and 4-methyl-resorcinol.

Examples of the aromatic dithiol compounds of the group (d₁) above arebenzene-1,4-dithiol, benzene-1,3-dithiol, 2,6-naphthalene-dithiol and2,7-naphthalene-dithiol.

Examples of the aromatic thiophenol compounds of the group (d₂) aboveare 4-mercaptophenol, 3-mercaptophenol and 6-mercaptophenol.

Examples of the aromatic thiol carboxylic acid compounds of the group(d₃) above are 4-mercapto-benzoic acid, 3-mercapto-benzoic acid,6-mercapto-2-naphthoic acid and 7-mercapto-2-naphthoic acid.

Examples of the aromatic hydroxyamine and aromatic diamine compounds ofthe group (e) above are 4-aminophenol, N-methyl-4-aminophenol,1,4-phenylenediamine, N-methyl-1,4-phenylenediamine,N,N′-dimethyl-1,4-phenylenediamine, 3-aminophenol,3-methyl-4-aminophenol, 2-chloro-4-aminophenol, 4-amino-1-naphthol,4-amino-4′-hydroxydiphenyl, 4-amino-4′-hydroxydiphenyl ether.,4-amino-4′-hydroxydiphenylmethane, 4-amino-4′-hydroxydiphenyl sulfide,4,4′-diaminophenyl sulfide (thiodianiline), 4,4′-diaminodiphenylsulfone, 2,5-diaminotoluene, 4,4′-ethylenedianiline,4,4′-diaminodiphenoxyethane, 4,4′-diaminodiphenylmethane(methylenedianiline) and 4,4′-diaminodiphenyl ether (oxydianiline).

The thermotropic liquid crystal polymer for use in the present inventioncan be produced from the above monomers by the use of variousesterification techniques including the melt acidolysis and slurrypolymerization processes.

The molecular weights of thermotropic liquid crystal polyesters suitablefor use in the present invention are each in the range of about 2000 to200,000, preferably about 4000 to 100,000. The molecular weights of theabove-mentioned compounds may be determined by various methods includingone in which a compressed film is prepared and the terminal groups ofthe film are determined by infrared spectroscopy, and another in whichGPC being the common measuring method is performed after the preparationof a solution of the compound.

Aromatic homo- or copolyesters each containing the monomer unitrepresented by the following general formula (1) as an essentialcomponent are preferred among the thermotropic liquid crystal polymersobtainable from the above monomers. It is preferred that this monomerunit be contained in each of the polymers in an amount of at least about30% by mole. An amount of at least about 50% by mol is more preferably.

The aromatic polyester especially preferred for use in the presentinvention is one having the repeating units with structures respectivelyderived from three different compounds, i.e., p-hydroxybenzoic acid,phthalic acid and biphenol and represented by the following formula (2).In this polyester represented by the following formula (2), therepeating units each having a structure derived from biphenol maypartially or wholly be replaced by the repeating units derived fromdihydroxybenzene. Further, the aromatic polyester also especiallypreferred for use in the present invention is one having the repeatingunits with structures respectively derived from two different compounds,i.e., p-hydroxybenzoic acid and hydroxynaphthalene-carboxylic acid andrepresented by the following formula (3).

The thermotropic liquid crystal polymers for use in the presentinvention may be employed either individually or in combination.

A reinforcement or filler may be added to the thermotropic liquidcrystal polymer in order to improve the heat resistance and mechanicalproperties thereof. Each of the reinforcement and the filler may befibrous or particulate or a mixture of fibrous and particulatematerials. Examples of the fibrous reinforcements include inorganicfibers such as glass, shirasu glass, alumina, silicon carbide, ceramic,asbestos, gypsum and metal (e.g., stainless steel) fibers and carbonfiber. Examples of the particulate reinforcements include metal oxidessuch as wollastonite, sericite, kaolin, mica, clay, bentonite, asbestos,talc, alminosilicate and other silicates, alumina, silicon oxide,magnesium oxide, zirconium oxide and titanium oxide, carbonates such ascalcium carbonate, magnesium carbonate and dolomite, calcium sulfate,calcium pyrophosphate, barium sulfate and other sulfates, glass beads,boron nitride, silicon carbide and sialon. These may be hollow (e.g.,hollow glass fiber, glass microballoon, shirasu balloon and carbonballoon). If desired, pretreatment may be conducted with a silane ortitanium coupling agent prior to the application of the abovereinforcements.

Conventionally employed additives such as an antioxidant and a heatstabilizer (e.g., hindered phenols, hydroquinone, phosphates and theirsubstitution products), an ultraviolet absorber (e.g., resorcinol,salicylates, benzotriazole and benzophenone), a lubricant and a moldreleasing agent, a dye (e.g., nitrocin.), colorants including a pigment(e.g., cadmium sulfide, phthalocyanine and carbon black), a flameretarder, a plasticizer and an antistatic agent may be added in anamount in which these are not detrimental to the objects of the presentinvention for imparting desired properties to the thermotropic liquidcrystal polymer. The reinforcement, filler and other additives can beadded in an amount of 80% by weight or less and preferably 70% by weightor less based on the total weight of the composition.

The above filaments may contain a surface treatment and an adhesive forcombination with other materials such as FRP and FRTP and a matrix.

In the processes A and B according to the present invention, the melt ofthe thermotropic liquid crystal polymer filament upon exiting the meltspinning nozzle is directly heated and/or the temperature of theatmosphere right under the nozzle is held high to thereby increase thedraft ratio at that place so that the molecular orientation isincreased.

In the conventional process for melt spinning the thermotropic liquidcrystal polymer, the orientation of the liquid crystal polymer entirelyrelied on the shear force in the nozzle. Under the assumption that thedispersion of the uniformity of the liquid crystal polymer isunavoidable to a certain extent as mentioned above, however, increasingthe shear force to the extremity leads to extrusion abnormalities suchas melt fracture at heterogeneous high-polymerization-degree parts andto filament breakage upon exiting the nozzle. This shear increasingmethod is not feasible on an industrial scale.

Thus, in the present invention, the thermotropic liquid crystal polymeris passed through the nozzle at a shear rate such that end breakage doesnot occur and thereafter the temperature of the molten polymer is heldhigh so as to increase the draft ratio, thereby obtaining a filamentassembly. In this process, although heterogeneoushigh-polymerization-degree parts undergoes such a high molecularorientation in the nozzle that the same drafting leads to a low draftratio, the above parts are generally narrow and substantially no defectsare observed in the filament assembly as a whole despite someirregularity in the filament denier. The filament drafted at such a highratio naturally has strength and elastic modulus higher than those ofless drafted filaments.

The advantages of the processes A and B according to the presentinvention reside in that fine denier can be realized by increasing thedraft ratio when comparison is made with the same nozzle. That is,conventionally, attempts have been made to use a nozzle as narrow aspossible (as narrow as 0.1 mm or less) for realizing fine denier becauseof the incapability of increasing the draft ratio. However, thisextremely lowers the productivity because the extrusion rate isproportional to fourth power of the nozzle diameter, and the smallnozzle diameter is likely to cause melt fracture and nozzle clogging.The small diameter is more disadvantageous than advantageous.

In the processes of the present invention in which the draft ratio isincreased, not only can the above drawbacks be avoided but also theincrease of the draft ratio leads to the increase of the take-up speed,thereby increasing the production speed.

The processes of the present invention are characterized by increasingthe draft ratio while holding the temperature of the atmosphere rightunder the spinning nozzle high.

The temperature of the atmosphere has been extensively studied. As aresult, it has been found that it is preferred that the temperature at apoint 50 mm under the nozzle be the melting point of the employedthermotropic liquid crystal polymer minus 150° C., especially minus 50°C., or higher. The melting point is measured by DSC.

At any rate, the temperature of the atmosphere is substantially lowerthan the melting point of the polymer. The increase of the draft ratioeffected despite the temperature being lower than the melting pointwould be attributable to that the filament per se has heat capacity evenif the temperature is lowered to some extent, the thermotropic liquidcrystal polymer can be deformed at temperatures lower than the meltingpoint, that the crystallization rate of the thermotropic liquid crystalpolymer is low, that the filament has a high melt strength because ofthe molecular orientation made in the filament to thereby haveresistance to nozzle breakage, etc. However, when the temperaturedecrease is extreme, the draft ratio cannot be increased probablybecause of the formation of a skin layer.

With respect to the temperature of the atmosphere, the terminology“right under the nozzle” means a location in close vicinity to thenozzle along the filament spinning direction. The above terminology isused because the filament is extruded from up to down. Thus, when thespinning is conducted from down to up, the location is right over thenozzle. When the spinning is conducted horizontally, the location isright beside the nozzle. In the present invention, these locations arecollectively referred to by the terminology “right under the nozzle”.

Either direct or indirect heating may be adopted for increasing thetemperature of the atmosphere. For example, hot air blow from the die,heat-medium heating and heat insulating mold are all effective. Thepolymer melt filament may be heated by infrared radiation (includinglaser radiation).

Particular heating means will be described in the Examples describedhereinafter.

An apparent draft ratio is calculated by dividing the spinning take-upvelocity by the flow velocity of the polymer flowing out of the nozzle.The apparent draft ratio may be defined as the square of the value of(nozzle diameter/filament diameter), which is, however, not appropriatebecause it ignores the density difference between the melt and thesolid.

In the present invention, the above appropriate apparent draft ratio isexpressed as the draft ratio.

The draft ratio cannot be increased in the conventional spinning of thethermotropic liquid crystal polymer filament. There are even techniquescharacterized by decreasing the draft ratio (for example, U.S. Pat. No.4,468,364).

Generally, the draft ratio of the spun thermotropic liquid crystalpolymer filament is in the range of 1 to 20 (e.g., Examples of JapanesePatent Laid-Open Gazette No. 114723/1977). In the present invention, adraft ratio of at least 30 is readily attained, a draft ratio of atleast 50 is preferred, and a draft ratio of at least 100 is alsoattainable by virtue of the particular means provided for increasing thedraft ratio.

From the viewpoint of the phenomenon observed in the vicinity of thenozzle in connection with the increase of the draft ratio, the thinningby drafting (thinning zone) ends within 100 mm under the nozzle in thespinning of the conventional thermotropic liquid crystal polymerfilament. In contrast, the thinning reaches about 200 mm, 300 mm underoptimum conditions, under the nozzle in the processes A and B of thepresent invention.

This is the factor permitting the increase of the draft ratio. Thefreedom from rapid thinning is also the factor preventing filament endbreakage.

A draft tension may be imparted to the filament by the frictional forceof the fluid caused to flow along the filament.

The above-mentioned hot air blown from the die for increasing thetemperature of the atmosphere right under the nozzle also serves toimpart the draft tension to the filament. That is, the hot air serves adouble purpose. Moreover, the hot air serves to entangle the filaments.The die resembling the conventional die for melt blow fabrication of anonwoven web of polypropylene or polyesters may be used in this process.

In the melt blow fabrication of a nonwoven web of anon-liquid-crystalline polymer, e.g., a polyolefin such as polyethyleneor polypropylene or a polyester, however, the hot air is used to thinthe filament and does not contribute to the improvement of the strengthand elastic modulus. In contrast, the thermotropic liquid crystalpolymer filament of the present invention is not thinned to such anextremely small filament diameter as in the melt blow of thenon-liquid-crystalline polymer. The present invention is different fromthe conventional melt blow in that a filament of high strength and highelastic modulus is obtained only by the spinning. Further, the presentinvention is different in that the amount of hot air is only a fractionof that employed in the melt blow of the nonwoven web. The processes forproducing a filament and an assembly according to the present inventionare entirely different in the object and effect from the above prior artbecause of the difference in the constitutional features attributed tothe use of the thermotropic liquid crystal polymer.

The melt blow die may be used as the spinning nozzle in the presentinvention. The conventional melt blow die has a ratio of nozzle length(L) to nozzle diameter (D), L/D, of about 10, and the diameter of thenozzle is about 0.5 mm. It has been found that the use of such a die asit is in the spinning of a nonwoven web of thermotropic liquid crystalpolymer filaments is very unfavorable. As a result of further extensiveinvestigations, it has been found that it is preferred that the diameterof the spinning nozzle be 0.3 mm or less, preferably 0.2 mm or less andstill preferably 0.15 mm or less. Also, it has been found that the ratioof nozzle length (L) to nozzle diameter (D), L/D, be preferably 5 orless and still preferably 3 or less.

The so-called suction box using method may be mentioned as anothermethod in which the fluid is utilized for imparting a draft tension tothe filament. This method has been employed in the production of a spunbonded nonwoven web. The use thereof in combination with the process ofthe present invention in which the temperature of the polymer is heldhigh right under the nozzle further improves the strength and elasticmodulus of the thermotropic liquid crystal polymer filament.

In the production of the conventional spun bonded nonwoven web of anon-liquid-crystalline polymer, e.g., a polyolefin such as polyethyleneor polypropylene or a polyester, the temperature is rather held lowright under the nozzle to thereby increase the orientation of thefilament for strength improvement.

In contrast, in the spinning of the thermotropic liquid crystal polymerfilament according to the present invention, the melting point of theliquid crystal polymer is so high that, when the temperature right underthe nozzle is low, a skin layer is formed at the surface of thefilament, thereby disenabling the draft ratio increase. Thus, in thepresent invention, the temperature of the polymer right under the nozzleis held high contrary to the conventional spun bonding to therebyproduce a filament assembly of high strength and high elastic modulus.Illustratively, by virtue of holding the temperature right under thenozzle, the thermotropic liquid crystal polymer filament of the presentinvention can have a strength as high as at least 5 g/d after thespinning and at least 20 g/d after the heat treatment, which strengthcannot be realized in the conventional process for producing a spunbonded nonwoven web. Thus, the effect of the present invention ismarkedly distinct. In the conventional spun bonding process, thestrength is about 2 g/d at the best.

The fluid is effective not only in drafting the above melt filament butalso in mutually entangling the filaments. Therefore, it is preferredthat the filaments be caused to arrive at a conveyor or an assembly moldprior to the drop of the flow velocity of the fluid.

The fluid is generally a gas such as air. When an oxidizing atmosphereis to be avoided, nitrogen gas may be used. When a surface treatment ofthe filament is conducted, a gas having surface treating activity suchas ozone may be mixed into the high-temperature atmosphere. The fluidnaturally may be a liquid. In the use of a liquid, a greater tractiveforce can be imparted to the filament. Filament surface treatments(adhesive for use in FRP or FRTP, adhesive for strengthening the mutualfilament bonding, etc.) may also be mixed into the liquid.

The above fluid may be recycled. The recycling includes not only therecycling of the fluid per se but also the recycling of the heattherefrom.

Besides the fluid, a draft tension can be imparted to the filament bythe frictional force of nip rolls and a set of rotary rolls. The use ofthe frictional force is advantageous in that a mechanically quantifieddraft ratio can be provided, thereby contributing to product qualitystabilization. However, this method is less effective in entangling thefilaments, so that it is needed to employ the same in combination withthe fluid using process.

In the use of the above method in combination with the fluid usingprocess, it is important to first carry out the drafting of the filamentwith the fluid.

The conventional thermotropic liquid crystal polymer filaments generallyhave voids. In contrast, substantially no void formation is recognizedin the filaments obtained by the processes of the present invention.This is, for example, apparent from the densities of the filaments. Forexample, it is recognized that the filament produced by the process ofthe present invention has a density about 1 to 2% higher than that ofthe filament produced by the conventional melt spinning process in whichthe spun filament is only cooled and wound without the application ofany heated high-speed fluid. This is because there is substantially novoid formation recognized. Naturally, micrographic observations offilament sections show the above fact.

In the process A of the present invention, the filament may be wound inthe form of a bobbin, a cone, a cheese or a hank according to theconventional take-up technique.

The heat treatment of the obtained filament may be performed, forexample, by heating the filament wound in the form of a hank in a hotair oven while applying a tension, so that a product of high strengthand high elastic modulus can be obtained.

In the process B of the present invention, the filaments are assembledby piling the same in a given mold (e.g., helmet-shaped mold) to therebyproduce a product of a prescribed shape. In this process, generally, theshape of the filament exiting the nozzle does not agree with that of theproduct mold, so that the mold is moved to thereby produce a filamentassembly with the given shape. When the product mold has a very largeshape, it may be rational to connect a flexible hose to a nozzle portionthrough which the filaments are blown and to move the nozzle.

Effective hear treatment of the thermotropic liquid crystal polymerfilaments may be conducted by rendering the product mold ventilative andcirculating hot air through the filaments piled in the mold.

Naturally, the product may be removed from the mold and heat treated. Inthis case, it is requisite that the filaments be entangled so well as toretain the shape of the product in cooperation.

The filaments may be assembled in a different manner in which thefilaments are piled at a given width on a traveling belt conveyor tothereby obtain a roll of continuous nonwoven web as a product.

With respect to the heat treatment of the nonwoven web product, thenonwoven web product is ventilative, so that the heat treatment may becarried out by using a porous pipe as the roll core and by blowing hotair out from inside the pipe in a heat treatment chamber.

The filaments of high strength and high elastic modulus as obtained inthe present invention are so rigid that it is difficult to mutuallyentangle them. Thus, the above filaments have not been available in theform of a filament assembly or nonwoven web which can be handled in anindependent body because of satisfactory entanglement of the filaments.

The diameter of the filament is important for ensuring satisfactoryentanglement. When the filament diameter is 50 μm or greater, therigidity would render the entanglement unsatisfactory. It is desiredthat the filament diameter be 30 μm or less and more preferably 25 μm orless.

In the present invention, the obtained filament assembly or nonwoven webcan be handled as an integrated body because of satisfactory mutualentanglement of the filaments. Further, when the resultant product isused as an independent body or a composite, the product strength can beimproved.

The filament diameter and length appearing herein have been measured inenlarged micrographs.

As another feature of the appearance of the filament according to thepresent invention, it is important that the filament be flexed orcurled.

The filaments are neither flexed nor curled in the simple piling of thefilaments obtained by the conventional melt spinning process.

The flex or curl (herein referred to as “curl ratio”) is defined asfollows.

An enlarged photograph is taken of a filament assembly as an object, andthe radii of curvature of the filaments constituting the filamentassembly are measured. The measurements are averaged and divided by thephotograph magnification to thereby express the curl ratio.

The curl ratio of the filament assembly of the present invention rangesfrom several millimeters to several tens of millimeters. There is nosample having a curl ratio of greater than 50 mm. In contrast, withrespect to filament assemblies composed of commercially availablethermoplastic liquid crystal polymers, most of them each have a curlratio of greater than 100 mm, and none has a curl ratio of less than 50mm.

The filament of the thermotropic liquid crystal polymer constituting thepresent invention must be one which can be treated to have high strengthand high elastic modulus.

The filament of the thermotropic liquid crystal polymer is characterizedby having high strength and high elastic modulus, which are obtained byheat treatment.

The tensile strength of the filaments composing the filament assembly ofthe present invention is at least 2.5 g/d, preferably at least 3 g/d andstill preferably at least 5 g/d. The highest value of the tensilestrength is generally 100 g/d or less. A heat treatment improves thetensile strength of the filaments to at least 8 g/d, preferably at least15 g/d and still preferably at least 20 g/d.

The tensile strength of the filaments according to the present inventionis measured by the following method.

Filaments are extracted from a filament assembly, and the diametersthereof are measured by the use of a microscope. The measurements areconverted to deniers.

The tensile strength (gram) of each of the filaments whose diametershave been measured is measured in accordance with JIS L-1069 and dividedby the above filament denier to thereby obtain the tensile strength ofthe filament. The average is calculated with respect to 20 filaments tothereby obtain the average tensile strength. The interchuck length isset at 20 mm, and the pulling rate is set at 20 mm/min.

The tension modulus is also important. The thermotropic liquid crystalpolymer filament of the present invention has a high tension modulus.The tension modulus increases to 2 to 3 times that before heat treatmentby heat treatment at least 85 g/d, preferably at least 150 g/d and stillpreferably at least 350 g/d.

The strength of the thermotropic liquid crystal polymer component of thefilament composed of a thermotropic liquid crystal polymer and anon-liquid-crystalline polymer can be calculated from the strength ofthe filament obtained by spinning only the non-liquid-crystallinepolymer under the same conditions and the ratio of the thermotropicliquid crystal polymer component.

Filament extraction is difficult because of the low strength and elasticmodulus from the conventional spun bonded and melt blown nonwoven websof polypropylene, polyesters and polyamides. In contrast, extraction isrelatively easy from the filament assembly of the present inventionbecause of the high strength and high elastic modulus of the filaments.

In the processes C and D of the present invention, an extrudablenon-liquid-crystalline polymer is mixed and spun for increasing theorientation of the thermotropic liquid crystal polymer in the nozzle, sothat the shear rate in the nozzle is increased, thereby realizing athermotropic liquid crystal polymer filament of high strength and highelastic modulus.

With respect to the thermotropic liquid crystal polymer, persons ofordinary skill in the art to which the invention pertains well know thatthe increase of the shear rate in the nozzle produces a strong filament.However, the increase of the shear rate causes extrusion abnormalitiessuch as melt fracture as mentioned above and thus filament end breakageat the nozzle. Therefore, conventionally, the spinning is conducted at ashear rate of about 10³/sec (see, for example, Japanese Patent Laid-OpenGazette No. 196716/1988).

In the present invention, even a thermotropic liquid crystal polymerhaving a large molecular weight can be stably spun at a shear rate of100,000/sec or higher by virtue of the mixing of the extrudablenon-liquid-crystalline polymer.

The part of the thermotropic liquid crystal polymer in the filament spunat the high shear rate naturally has excellent molecular orientation andthus high strength and high elastic modulus.

Generally, it is known that the melt spinning of a mixture of lowmolecular weight and high molecular weight polymers at a high shearlocalizes the low molecular weight polymer in the vicinity of the innerwall of the nozzle, so that the surface of the spun filament is mainlycomposed of the low molecular weight polymer. In the processes of thepresent invention comprising mixing of the non-liquid-crystallinepolymer, however, similar phenomena occur without regard to themagnitude of the molecular weight, the spinning can be conducted at ahigh shear rate, and a markedly high draft ratio can be attained.

It is feasible not only to have a filament formed if a mixture of thethermotropic liquid crystal polymer and the non-liquid-crystallinepolymer but also to mix the thermotropic liquid crystal polymer filamentwith the non-liquid-crystalline polymer filament to thereby obtain amultifilament. In the latter, it is needed that the thermotropic liquidcrystal polymer filament be strong.

As expressed by the following formula, the shear rite (γ) is inverselyproportional to third power of the radius of nozzle (r) while theextrusion rate (Q) is proportional to the shear rate.

γ=4Q/πr ³

The above formula shows that the decrease of the nozzle diameter forobtaining a fine denier filament increases the shear rate to therebyincrease the possibility of end breakage.

With respect to the nonwoven web obtained by spinning a mixture with apolymer having no liquid crystal properties (EP), it has been foundthat, besides the realization of a high shear rate, a high draft ratiocan be attained, and that a fine fiber of high strength can be realizedwithout the need to resort to high shear rate. That is, in the filamentspun through the nozzle, the EP migrates to the surface by virtue of theshear rate in the nozzle and the subsequent draft so as to preventformation of a skin of TLCP on the surface with the result that a highdraft ratio can be realized. The spinning of the above mixture ensuresready realization of a draft ratio of at least 50, especially at least100. This high draft ratio leads to realization of a high strength.

Further, it is advantageous to provide means for holding the filamentspun right under the spinning nozzle at a high temperature according tothe present invention for realizing a high draft ratio. Still further,the draft ratio can effectively be increased by the employment of acomposite fiber having a core-sheath structure in which EP forms thesheath while TLCP forms the core.

Therefore, the processes C and D of the present invention not onlyproduce filaments of high strength and high elastic modulus but alsoincrease the production volume by several times.

The mixing including kneading is represented by the term “mixing” forsimplicity herein, and in the present invention at least two polymersmust be satisfactorily mixed. When the degree of mixing isunsatisfactory, only the thermotropic liquid crystal polymer (TLCP) isextruded in some parts while only the extrudable polymer (EP) isextruded in some other parts, so that the object of the presentinvention cannot be attained.

Even at the stage of the mixing of starting material pellets, a uniformmixing must be accomplished. The extruder suitable for use in thepresent invention includes single and double-screw extruders and furthera vent type extruder. The extruder is preferably provided with a gearpump for ensuring the quantification of the extrusion rate. Further, itis advantageous to effect highly mixing with a static mixer upon theexiting from the extruder or just before the nozzle.

There are other systems of mixing of the thermotropic liquid crystalpolymer and the extrudable non-liquid-crystalline polymer in thefilament, which include those such as a fiber having a sectionalstructure like islands being scattered in a sea (island-in the seastructure), a split fiber and a multilayer fiber employed in theproduction of a synthetic leather from the conventional fine fiber ofpolyethylene terephthalate.

With respect to the mixed extrudable non-liquid-crystalline polymer,various types may be used as long as the melt fracture is not caused ata high shear rate.

The non-liquid-crystalline polymer serves a double purpose if not onlyis it used for effecting the high shear rate but also it functions as amatrix resin or an adhesive polymer for bonding with a matrix resin inthe use of the thermotropic liquid crystal polymer filament of thepresent invention as a reinforcing filament in FRTP or FRP. In thelatter, the miscibility with the matrix resin is improved.

The extrudable non-liquid-crystalline polymer for use in FRTP is, forexample, polyethylene terephthalate (PET) or polybutylene terephthalate(PBT), which exhibits excellent miscibility with the thermotropic liquidcrystal polymer. A polyolefin resin, e.g., PP or PE modified with anacid such as maleic acid is suitable for use in the FRTP based onpolypropylene (PP). Further, various thermoplastic polymers such aspolycarbonates, polyamides and polyolefins may be used as the extrudablenon-liquid-crystalline polymers.

Slow curing resins, epoxy resins having low curing agent contents,unsaturated polyester resins and phenolic resins may be used as theextrudable non-liquid-crystalline polymers for use as the matrix resinsin the FRP.

The non-liquid-crystalline polymer used herein is a resin which isextrudable and which does not exhibit optical anisotropy when beingmelted. Examples of the resins include polyolefins such as polyethyleneand polypropylene; acid-modified polyolefins obtained by modifying thepolyolefin by copolymerization or graft polymerization with maleicanhydride, acrylic acid, methacrylic acid, unsaturated esters such asmethyl esters thereof, vinyl acetate or other unsaturated acids;polyesters such as polyethylene terephthalate and polybutyleneterephthalate; polystyrene; polyvinyl chloride; ABS resin; nylon andother polyamides; polycarbonates; polysulfides; polyphenylene ether; andpolyether ether ketone (PEEK). Of these, polyolefins, acid-modifiedpolyolefins and polyesters are preferred.

The thus mixed thermoplastic resin is extruded in the form of afilament, which is optionally cut into fixed lengths. The resultantfilament is used as a reinforcing fiber in FRP or FRTP. It is desiredthat the thermoplastic resin be a matrix resin for the FRP or FRTP. Itis also desirable that the resin be a polymer compatible with the matrixresin.

When the mixed thermoplastic polymer is to be finally removed, this canbe easily accomplished while being heated at the stage of the heattreatment of the thermotropic liquid crystal polymer filament.

With respect to the mixing proportion, the extrudablenon-liquid-crystalline polymer may be mixed in an amount of 10% byweight or less when the polymer is finally to be removed or when thepolymer is allowed to remain in the final product but only for use as anadhesive with the matrix. On the other hand, when the polymer is used,without being removed, as a matrix resin in FRP or FRTP, thenon-liquid-crystalline polymer may be mixed in an amount as large as 50to 98% by weight. That is the mixing ratio of the thermotropic liquidcrystal polymer to the extrudable non-liquid-crystalline polymer is0.5:99.5 to 99.5:0.5 (on the weight basis).

In the present invention, combining the processes A and B with theprocesses C and D is advantageous. In particular, when the amount of theextrudable non-liquid-crystalline polymer is small in the process C andD, the combination with the processes A and B is especiallyadvantageous.

The localization of much of the extrudable non-liquid-crystallinepolymer component at the surface of the filament as mentioned aboveprevents the formation of a skin layer at the surface of thethermotropic liquid crystal polymer filament. This is also advantageousfrom the viewpoint of the increase of draft ratio.

In FRP or FRTP, the thermotropic liquid crystal polymer filament and thematrix polymer should be uniformly distributed. As a means foruniforming the distribution, the matrix resin for use in FRP or FRTP ora polymer having affinity for the matrix resin may be filamentous andmixed with the thermotropic liquid crystal polymer filament in thefilament assembly to thereby effect uniform mixing with the matrixpolymer.

In this process, the matrix polymer to be mixed should be an extrudablenon-liquid-crystalline polymer, this polymer being extruded throughanother nozzle. Often, the combination with the processes A and B of thepresent invention is advantageous. The extrudable non-liquid-crystallinepolymer to be discharged through the nozzle need not account for thewhole of the matrix of the FRP or the like as the final product. In thefabrication of FRP or the like, another matrix may be added to therebyshape the FRP or the like.

In the filament assembly, the filaments may be arranged in the desireddirection to thereby produce an assembly ensuring effective exertion ofthe capabilities of the filaments of high strength and high elasticmodulus.

Although the thermotropic liquid crystal polymer filaments of thepresent invention are characterized by the high orientation of themolecules, the capabilities thereof may be highly exerted by arrangingthe filaments. A complete arrangement of the filaments as in the prepregis not needed. It is satisfactory for 70 to 80% of the constituentfilaments to arrange in a given direction. Although the direction of thearrangement is not particularly limited as long as the arrangement ismade in a given direction, the arrangement in the longitudinal direction(along the line) or the transverse direction is preferred in acontinuous web being in the form of a nonwoven web.

The arrangement of the filaments in the desired direction enables thefilament assembly to effectively exert the capabilities of the filamentsof high strength and high elastic modulus.

The conventional arranged nonwoven webs have been produced by orientinga nonwoven web composed of a thermoplastic polymer or by solutionspinning of a cellulosic polymer (Japanese Patent Laid-Open Gazette No.148861/1989 and U.S. Pat. No. 5,312,500).

In the present invention, orienting means is not particularly needed. Anarranged nonwoven web can be produced by applying orthogonal or crossedhot air to vibrating molten filaments.

Further, in the present invention, the thermotropic liquid crystalpolymer filament can be mass produced at a reduced cost by causing theflow velocity of the fluid to impart the take-up tension for meltspinning of the thermotropic liquid crystal polymer and by accommodatingthe spun filament in a container such as a box or a can.

The accommodation of the spun filament in a box or other containers isregarded as an effective means taking advantage of the propertiespeculiar to the thermotropic liquid crystal polymer filament because ahighly oriented filament can be obtained only by spinning of thethermotropic liquid crystal polymer filament and because the subsequentheat treatment can be conducted for the filament while beingaccommodated in the box or other containers. Further, the aboveaccommodation method is especially advantageous in the industrial massproduction. In the production of pile or chopped strands by subsequentlycutting the thermotropic liquid crystal polymer filament, this take-upand accommodation method is especially advantageous because rareoccurrence of breakage is usually not significantly detrimental to theproduct quality.

Heat treatment of the filament by rendering the above container such asa can or a box ventilative, for example, by providing the wall of thebox with porosity and then by circulating hot air within the containerholding the filament therein is also an effective heat treatment methodfor the thermotropic liquid crystal polymer filament. When the filamentis in the form of a bobbin, it is difficult to uniform the temperaturedown to the core. Even if the temperature is uniformed, the heatingperiod is different according to portions, thereby causing the effect ofthe heat treatment to be different according to portions. In the bobbin,the strength and elastic modulus of the filament at the surface aredifferent from those at the core.

Heat treatment improves the strength and elastic modulus of the filamentspun by the processes of the present invention. Especially, theimprovement of the strength is marked.

The heat treatment may be conducted in the form of not only the filamentbut also a woven web, chopped strands, a nonwoven web or a shapedarticle such as FRP or FRTP.

The heat treatment of the shaped filament assembly may be conductedeither inside the mold or outside the mold. A roll of, for example, anonwoven web may undergo heat treatment in the form of the roll asmentioned hereinbefore. Alternatively, the nonwoven web may be unrolledin a heat treatment chamber and heat treated.

Further, the nonwoven web may be heat treated during the continuous flowthereof.

The shaped article such as FRP may be heat treated in the form of theshaped article.

Even the filament having been just spun according to the presentinvention and having not yet undergone heat treatment has a certainlevel of strength, and especially its elastic modulus is high, so thatit can often be put in practical use without any heat treatment or onlywith some heat inevitably applied thereto in the subsequent steps.

In the formation of FRP or the like, the filament assembly of thepresent invention may be mixed with a matrix and heat pressed (when thefilament assembly is produced according to the processes C and D andthus already contains a matrix, the above mixing is omitted and thefilament assembly is heat pressed as it is).

The filament assembly of the present invention together with a matrixresin may be formed into a sheet for use as a stampable sheet.

The filament assembly of the present invention may not need a matrix asdifferent from FRP and FRTP and may independently be used as a beatinsulating material, a sound absorbing material, a filter or the like.

In the present invention, a filament assembly of high strength and highelastic modulus is directly obtained from the spinning stage, so thatthe cost of the filament assembly per se is low. Further, the filamentassembly of the present invention may be treated with an adhesive foruse as a reinforcing fiber for FRP or the like, the uniformdispersibility thereof may be high, it may reduce the fiber usage andthe filament assembly may have a product shape. Therefore, the costs forobtaining the final product can be reduced.

The filament assembly of the present invention may be in the form of anindependent article shaped like a helmet, a container for high voltagetransformer, an automobile bumper, a filter, a heat insulating material,a cloth, a sheet, a plate or a pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of one form of apparatus adapted to effect heatingright under a nozzle with hot air, which shows one mode of process forforming a helmet-shaped filament assembly;

FIG. 2 is a view of a lower side of the spinning apparatus 2 shown inFIG. 1;

FIG. 3 is a view of one form of apparatus adapted to effect heatingright under a nozzle with hot air, which shows one mode of the process Aof the present invention;

FIG. 4 is a view of one form of spinning apparatus adapted to heat amolten filament 34 under a nozzle 32 of a spinning machine 31 by meansof an infrared heater 33;

FIG. 5 is a view showing one mode of process for producing a filamentassembly in the form of a nonwoven web with the use of a die for meltblow nonwoven-fabric production;

FIG. 6 shows a view of a section (FIG. 6A) and a view of an innerstructure (FIG. 6B) of the melt blow die of FIG. 5;

FIG. 7 is a view of one form of nozzle part of the conventional meltblow die;

FIG. 8 is a view of one form of nozzle part of a melt blow die suitablefor use in the present invention;

FIG. 9 is a view of an apparatus provided with a heat insulating mold 62and a ventilative box 66 under a die for spun bonded nonwoven webproduction 61, which shows another mode of the process of the presentinvention;

FIG. 10 is a view of a filament assembly separated from the box 66 ofFIG. 7;

FIG. 11 is a view of a lower side of the spun bonding die 61 of FIG. 7;

FIG. 12 is a view of a section of a suction box 64 of FIG. 7 as observedalong the direction A of FIG. 8;

FIG. 13 is a view of one form of apparatus for use in co-extruding athermotropic liquid crystal polymer and an extrudablenon-liquid-crystalline polymer to thereby produce one form of filament;

FIG. 14 is a view of one form of apparatus for use in extruding athermotropic liquid crystal polymer and an extrudablenon-liquid-crystalline polymer to thereby produce one form of filamentby the use of two extruders;

FIG. 15 is a view of an upper side of an extrusion die 115 of FIG. 14;

FIG. 16 is a view of an inner structure of a filament composed of acomposite fiber having a sheath-core structure obtained according to onemode of process of the present invention;

FIG. 17 is a perspective view of filaments obtained by the use ofvarious types of nozzles;

FIG. 18 is a view of another form of apparatus for use in extruding athermotropic liquid crystal polymer and an extrudablenon-liquid-crystalline polymer to thereby produce one form of filamentby the use of two extruders;

FIG. 19 is a view of a filament with which secondary air is collidingand crossing; and

FIG. 20 is a schematic view of a nonwoven web arranged according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, embodiments of the present invention will be described indetail with reference to the drawings.

Examples 1 to 5 and Comparative Examples 1 to 3

Production of Filament Assembly

FIG. 1 shows one mode of the process B of the present invention in whicha helmet-shaped filament assembly is produced by carrying out heatingright under a nozzle with hot air.

Referring to FIG. 1, a melt of thermotropic liquid crystal polymer 1 isquantitatively fed to a spinning apparatus 2 by means of an extruder anda gear pump (both not shown). A molten filament 4 is extruded through anozzle 3. Hot air of high pressure 5 is fed to the spinning apparatus 2and blown through an aperture 6 provided in close vicinity to the nozzlealong the filament 4. Even if hot air is blown, it catches up cold airtherearound to thereby become 40 to 50° C. air several tens ofmillimeters under the nozzle. Thus, the melt is solidified to become afilament 7, which is piled on a helmet-shaped mold 8, so that a filamentassembly 9 is obtained. The helmet-shaped mold 8 is moved so as for thefilament to uniformly pile on the mold (when thicker parts are desired,so moved).

A thermocouple 10 with a thin tip (1 mm in diameter) is disposed at aposition 50 mm under the nozzle (when the nozzle is directed downward)to thereby measure the temperature there.

The thermocouple 10 is to be as small as possible so as to sensitivelydetect the temperature. The measuring time is set at 3 min to preventthe temperature of the thermocouple from going up by the radiant heatfrom the spinning apparatus 2.

FIG. 1 shows the use of a single nozzle. A plurality of nozzles may beused in combination.

FIG. 2 is a view of a lower side of the spinning apparatus 2 of FIG. 1.In FIG. 2A, the aperture for hot air 6 opens around the nozzle 3. FIG.2B shows another form in which a plurality of small apertures for hotair 21 open in a line besides the aperture for hot air 6. FIG. 2C showsstill another form in which a plurality of small apertures for hot air22 are circularly disposed.

These pluralities of small apertures 21, 22 cause the molten filament 4to vibrate, so that the frictional resistance attributed to the airbrought into contact with the molten filament 4 is increased to therebyincrease the draft ratio.

Various experiments were conducted by the use of the apparatus shown inFIGS. 1 and 2. With respect to representative ones, Table 1 shows theproperties of spun filaments in relation to the experimental conditions(Examples 1 to 5 and Comparative Examples 1 to 3).

TABLE 1 Temp. of Extrusion Share Temp. of Flow rate N50 Diam. of CurlType of Shape of resin rate rate hot air of hot air temp. filament Draftas spun ratio polymer nozzle ° C. g/min L/sec ° C. L/min ° C. μ ratiostrength mm Example 1 a I 380 6.9 4.3 × 10⁴ 400 70 259 39 59 3.2 6 2 aII 380 1.1 2.4 × 10⁴ 400 90 298 25 64 4.9 1.2 3 a III 380 0.3 6.6 × 10³400 90 298 30 44 4.0 2.5 4 b II 420 0.3 6.6 × 10³ 450 110 345 39 26 4.78 5 c II 400 0.3 6.6 × 10³ 450 110 345 34 34 3.2 15 Comp. Example 1 a II380 1.1 2.4 × 10⁴ — 0 120 185 1.2 0.7 210 2 a II 380 1.1 2.4 × 10⁴ 30090 191 139 2.0 2.1 87 3 a II 380 0.5 5.0 × 10⁴ — 0 127 81 1.7 2.3 170

In Table 1, the column “type of polymer” specifies the type of employedthermotropic liquid crystal polymer as follows:

a: thermotropic liquid crystal polyester being tetracopolyester havingrepeating units respectively derived from terephthalic acid, isophthalicacid, 4-hydroxybenzoic acid and 4,4′-dihydroxydiphenyl (molarratio=0.6/0.4/2/1) which has a melting point of 350° C. (measured byDSC),

b: thermotropic liquid crystal polyester being tercopolyester havingrepeating units respectively derived from terephthalic acid,4-hydroxybenzoic acid and 4,4′-dihydroxydiphenyl (molar ratio=1/2/1)which has a melting point of 400° C. (measured by DSC), and

c: thermotropic liquid crystal polyester being bicopolyester havingrepeating units respectively derived from 4-hydroxybenzoic acid and6-hydroxy-2-naphthoic acid (molar ratio=7/3) which has a melting pointof 280° C. (measured by DSC).

The shape of nozzle is as follows:

I: 0.3 mm in nozzle diameter and 0.3 mm in nozzle length (FIG. 2A),

II: 0.2 mm in nozzle diameter and 0.2 mm in nozzle length (FIG. 2B), and

III: 0.12 mm in nozzle diameter and 0.2 mm in nozzle length (FIG. 2A).

The temp. of resin is the temperature of the resin fed from theextruder, and the temperature of the spinning apparatus 2 is set nearlyat this temperature.

The extrusion rate (g/min) and the flow rate of hot air (liter/min) arethe rates per nozzle. The N50 temp. indicates the temperature of theatmosphere at a position 50 mm under the nozzle.

The as spun strength is the strength of the filament upon spinningthereof in terms of g/d (grams per denier).

In the Table, all the experiments except for Comparative Example 3 werecarried out for obtaining a filament assembly. In Comparative Example 3,the spun filament was taken up by a winder while increasing the shearrate and the draft ratio so as to obtain a filament of maximizedstrength and elastic modulus as in the conventional filament producingexperiment. In Comparative Example 3, even if use was made of a nozzleof 0.12 mm, the strength and the draft ratio were 2.3 g/d and 1.7,respectively. In contrast, in Example 2 in which use was made of anozzle of 0.2 mm in diameter, the strength and the draft ratio increasedto 4.9 g/d and 64, respectively.

In the long-term operation, nozzle cloggings are more frequent at 0.12mm in diameter than at 0.2 mm in diameter by a figure or more.

The filament assembly of Example 1 appearing in Table 1 was photographedat 15 magnifications and observed. As a result, it has been found thatthe constituent filament assembles each have a diameter of about 25 μmand that the filament curls are distributed from about 5 mm to 50 mm inradii of curvature (0.3 to 3 mm because of 15 magnifications, averagingto give a curl ratio of 1.2 mm).

For comparison, a bundle of 40 5-denier commercially availablethermotropic liquid crystal polymer filaments (trade name: Vectran soldby Kuraray Co., Ltd.) (200 denier in total) was loosened to therebyobtain an assembly sample. This was also photographed at 15magnifications and observed. As a result, it has been found that thereis no filament entanglement with most of the filaments beingsubstantially straight, and that the filament bundle loosening is notsatisfactory to cause bundled parts to remain. Such unloosened bundledparts of filaments have poor resin infiltration at the use in FRP ofFRTP and occasionally invite defects such as taking up of bubbles.

Thus, only assembly of commercially available thermotropic liquidcrystal polymer filaments does not lead to satisfactory entanglement.The assembly cannot independently be handled as a whole, and thehandling immediately causes configuration collapse. An adhesive may beapplied for bonding. However, the use of a heat-resistant adhesiveincreases the cost. Further, the adhesive gravely degrades the heatresistance and electrical properties of the filaments. The curl ratio ofthe comparative filaments was 100 mm or more as measured byphotographing at less magnification.

Determination of Density

The densities of the filament of Example 1 and a filament produced bythe conventional melt spinning method in which the spun filament wassimply cooled and wound (use was made of the same thermotropic liquidcrystal polymer as in Example 1) were measured by the density gradienttube method. As a result, it has been found that the filament of Example1 has a density of 1.348 which is about 1% higher than the density ofthe filament produced by the conventional melt spinning method, 1.371.However, there was no significant difference between the true specificgravities of the filament of Example 1 and the filament produced by theconventional melt spinning method.

Sectional micrographs showed the presence of voids in the filamentproduced by the conventional melt spinning method but substantially novoids in the filament of Example 1.

Examples 6 to 10 and Comparative Examples 4 to 6

Production of Filament

FIG. 3 shows one mode of the process A of the present invention in whichheating right under a nozzle is conducted with hot air.

Referring to FIG. 3, a melt of thermotropic liquid crystal polymer 1 isquantitatively fed to a spinning apparatus 2 by means of an extruder anda gear pump (both not shown). A molten filament 4 is extruded through anozzle 3. Hot air of high pressure 5 is fed to the spinning apparatus 2and blown through an aperture 6 provided in close vicinity to the nozzlealong the filament 4. Even if hot air is blown, it catches up cold airtherearound to thereby become 40 to 50° C. air several tens ofmillimeters under the nozzle. Thus, the melt is solidified to become afilament 7, which is taken up around a winder 51.

FIG. 2 is a view of a lower side of the spinning apparatus 2 shown inFIG. 3.

Various experiments were conducted by the use of the apparatus shown inFIGS. 3 and 2. With respect to representative ones, Table 2 shows theproperties of spun filaments in relation to the experimental conditions(Examples 6 to 10 and Comparative Examples 4 to 6).

TABLE 2 Temp. of Extrusion Share Temp. of Flow rate N50 Diam. of Type ofShape of resin rate rate hot air of hot air temp. filament Draft as spunpolymer nozzle ° C. g/min L/sec ° C. L/min ° C. μ ratio strength Example 6 a I 380 6.9 4.3 × 10⁴ 400 20 235 37 67 3.5  7 a II 380 1.1 2.4 × 10⁴400 20 272 22 83 5.2  8 a II 380 0.3 6.6 × 10³ 400 20 272 26 59 4.1  9 bII 420 0.3 6.6 × 10³ 450 20 316 34 34 4.8 10 c II 400 0.3 6.6 × 10³ 45020 316 31 42 3.7 Comp. Example  4 a II 380 1.1 2.4 × 10⁴ — 0 120 120 2.81.8  5 a II 380 1.1 2.4 × 10⁴ 300 20 191 85 5.5 2.1  6 a II 380 0.5 5.0× 10⁴ — 0 127 81 1.7 2.3

In Table 2, the types of polymers and the conditions such as the shapeof nozzle are the same as employed in Table 1.

FIG. 4 shows another mode of the process B of the present invention inwhich a molten filament 34 is heated under a nozzle 32 of a spinningmachine 31 by means of an infrared heater 33. A reflector 35 is disposedaround the infrared heater 33 in order to improve the heatingefficiency.

The filament 34 is taken up by driven rollers 36, 37 and piled on ahelmet-shaped mold 8 to thereby produce a filament assembly 9. In thisprocess, a negative pressure chamber 39 may be provided on the back ofthe mold 8 by suctioning air 38 so that a filament assembly 9 havinghigh density is produced.

A static mixer 40 may be disposed in the spinning machine 31, so thatthe temperature is uniformed in the extruder and the spinning machine 31to thereby ensure extrusion at uniform temperature. As a result, theshear rate can be increased, and a high draft ratio can be realized.Thus, the quality of the filament assembly is improved and stabilized.

FIG. 5 shows one mode of the process B of the present invention in whicha filament assembly in the form of a nonwoven web is produced with theuse of a die for melt blow nonwoven-web production.

Filaments 43 are extruded through a vast plurality of minute apertures42 of the melt blow die 41, and hot air 46 is blown through slits 44, 45provided on both sides of each of the minute apertures.

The filaments 43 are drafted by the frictional force attributed to thevelocity of hot air to thereby orient the molecules and entangled andpiled on a conveyor belt 47 as a filament assembly 48 in the form of anonwoven web by the power of the hot air.

The filament assembly 48 is carried by the traveling conveyor belt 47and passed through a vast plurality of turn rolls 50 while gaining timein a heat treatment chamber 49 in which hot air is circulated. Theresultant heat treated filament assembly 52 is taken up by a winder 51.

When the entanglement of the filaments is poor in the filament assemblywhich has exited the conveyor belt 47, the integration thereof may bepromoted by needle punching or by the use of a heat-resistant adhesive(e.g., ceramic adhesive).

FIG. 6 shows a section of the melt blow die (FIG. 6A) and an innerstructure thereof (FIG. 2B). The die is heated by a heating block 53.

FIG. 7 shows one form of the structure of the nozzle part 42 of theconventional melt blow die of FIG. 6, in which the nozzle diameter is0.5 mm with the ratio of nozzle length (L) to nozzle diameter (D), L/D,being 10. This nozzle is extremely unsuitable for the spinning of thethermotropic liquid crystal polymer filament.

FIG. 8 shows one form of the structure of the nozzle part of the meltblow die which is suitable for use in the present invention. The nozzlediameter is 0.15 mm and L/D is 2.

In the conventional production of a melt blow nonwoven web ofpolypropylene or polyesters, use is made of a die having a spinningnozzle diameter of about 0.5 mm for resisting the draft force byhigh-velocity air. When the diameter is smaller, breakages at the nozzlebecome frequent and the occurrence of shot is increased, so that anonwoven web of high quality cannot be obtained. In the conventionalmelt blow die, L/D is generally about 10 taking into account thelinearity and mechanical pressure resistance of the spun filament. Thestrength of the filaments composing the melt blown nonwoven web ofpolypropylene or polyesters produced with the use of the aboveconventional die is nearly entirely nil, 0.5 g/d or less at the best.

In the spinning of the nonwoven web of TLCP according to the presentinvention, however, the strength of the extruded filament is as high as2.5 g/d or greater, so that, even if the spinning nozzle diameter issmall, breakages at the nozzle is less frequent. As a result of variousexperiments, it has been found that it is preferred that the nozzlediameter be 0.3 mm or less, preferably 0.2 mm or less and stillpreferably 0.15 mm or less. When the nozzle diameter is too small,cloggings become frequent to disadvantage in practice. Therefore, thenozzle diameter is generally not smaller than 0.005 mm.

With respect to the nozzle for use in the present invention, the smallerthe value of L/D, the less frequent the filament breakage, with theresult that a nonwoven web of high-quality filaments is obtained.However, rendering the value of L/D 0.1 or less is difficult from theviewpoint of the pressure resistance of the spinning machine. As aresult of various experiments, it has been found that it is preferredthat L/D be 5 or less and preferably 3 or less.

FIGS. 9 to 11 show another mode of the process D of the presentinvention in which a heat insulating mold 62 is disposed under a die forspun bonded nonwoven web production 61, and in which a filament 63extruded through the die 61 is not cooled by virtue of the heatinsulating mold, taken up by an air 65 of a suction box 64 and piled ina ventilative box 66 to thereby obtain a filament assembly 67. In thefilament assembly 67, the filaments are mutually entangled by the powerof the air. When the entanglement is not satisfactory, the integrationof the filament assembly can be strengthened with the use of, forexample, a heat-resistant adhesive (e.g., ceramic adhesive).

The box 66 is ventilative, so that it can be brought as it is into a hotair circulating chamber for heat treatment. Then, a heat-treatedfilament assembly 71 (FIG. 10) is separated from the box. The filamentassembly 71 is used, as it is or after rework, as an adiabatic filter,an adiabatic mat or the like.

The heat insulating mold 62 is one composed of a lower part of the spunbond die 61 surrounded with an adiabatic material. Preferably, the heatinsulating mold 62 per se is positively heated with a heater.

FIG. 11 is a view of a lower side of the spun bond die 61. There are avast plurality of nozzles 81, and they are not arranged in a line asdifferent from the melt blow die. This is advantageous from theviewpoint that the number of nozzles can be increased to improveproductivity. The conventional die for spinning synthetic polypropyleneor polyethylene terephthalate multifilaments may be used as the abovedie.

FIG. 12 is a view of a section of the suction box 64 as observed alongthe direction A of FIG. 9. The thermotropic liquid crystal polymerfilament 63 introduced through an inlet 91 is speedily drawn in a slit94 by an air 65 having its pressure uniformed in an air reservoir 92 andhaving speeded up in an air slit 93. Thus, the filament undergoes amolecular orientation.

Examples 11 to 15

Production of Filament Assembly

FIG. 13 shows one mode of the process D of the present invention, inwhich a thermotropic liquid crystal polymer and extrudablenon-liquid-crystalline polymer are mixed together and extruded tothereby mix the thermotropic liquid crystal polymer and the extrudablenon-liquid-crystalline polymer into a filament. Pellets 102 composed ofa thermotropic liquid crystal polymer mixed with an extrudablenon-liquid-crystalline polymer in a given ratio are stocked in a hopper101 (preferably drying hopper 101).

The pellets 102 are kneaded by means of a screw 104 in an extruder 103,further mixed by means of a static mixer 105 and fed to a spun bond die61 by means of a gear pump 106. A filament 107 spun by the spun bond die61 is carried through a heat insulating mold 62 and a suction box 64disposed under the die and piled on an automobile bumper mold 108 in theform of an assembly 109 of the filament composed of the thermotropicliquid crystal polymer mixed with the extrudable non-liquid-crystallinepolymer.

The extrusion rate is maximized so as for the shear rate to be high atthe nozzle 81 (FIG. 11) of the spun bond die 61, thereby improving themolecular orientation of the thermotropic liquid crystal polymer part.

A matrix having, for example, a filler and a foaming agent mixedthereinto may be added to the filament assembly 109 accommodated in themold 108 and heated to thereby carry out both of heat treatment of thethermotropic liquid crystal polymer and molding of the bumper.

FIG. 17D shows a section of the filament composing the filament assembly109. It is apparent therefrom that the thermotropic liquid crystalpolymer having undergone a high molecular orientation is dispersed inthe extrudable non-liquid-crystalline polymer.

The results of mix spinning experiments conducted with the use of theapparatus of FIG. 13 are shown in Table 3 (Examples 11 to 15).

TABLE 3 Temp. of Extrusion Share Diam. of TLCP EP resin rate ratefilament Draft as spun Example Type of polymer % Type of polymer ° C.g/min L/sec μ ratio strength 11 c 50 t 380 250 1.5 × 10⁶ 31 94 4.7 12 c75 n 380 34 2.2 × 10⁵ 37 66 4.5 13 c 25 p 380 41 2.5 × 10⁵ 23 170 4.9 14c 75 n 400 70 4.4 × 10⁵ 55 33 4.7 15 c 25 t 350 36 2.2 × 10⁵ 42 51 3.2TLCP: thermotropic liquid crystal polymer EP: extrudablenon-liquid-crystalline polymer

The nozzle diameter was 0.3 mm and the land length 2 mm, and 400 nozzleswere provided.

The same type of thermotropic liquid crystal polymer as in Table 1 wasemployed, and the types of employed extrudable non-liquid-crystallinepolymers were as follows:

p: polypropylene MFR 0.4 g/10 min

n: maleic acid-modified polyethylene MFR 1.0 g/10 min

(1% by weight of maleic anhydride was added to high densitypolyethylene)

t: PET resin (polyethylene terephthalate)

The extrusion rate is expressed by g/min per nozzle.

Provided that q, fo and fe are respectively defined as the mixing ratioof thermotropic liquid crystal polymer, the as spun strength of mixedfilament and the strength of the filament obtained by spinning theextrudable non-liquid-crystalline polymer only under the sameconditions, the strength of the thermotropic liquid crystal polymerfilament only, fs, satisfies the following equality:

fs={fo−fe(1−q)}/q.

Table 2 demonstrates that all the shear rate, the draft ratio and the fsstrength are improved by the mixing of the extrudablenon-liquid-crystalline polymer.

Examples 16 to 20

Production of Filament

FIG. 13 shows one mode of the process C of the present invention, inwhich a thermotropic liquid crystal polymer and a non-liquid-crystallinepolymer are mixed together and extruded. The employed apparatus issimilar to that of FIG. 13. Pellets composed of a thermotropic liquidcrystal polymer mixed with a non-liquid-crystalline polymer in a givenratio are stocked in a hopper, kneaded by means of a screw in anextruder, further mixed by means of a static mixer and fed to a die bymeans of a gear pump.

Although the spun bond die of FIG. 11 was used as the above die, it isnot critical and other general dies for use in the melt spinning of, forexample, polyethylene terephthalate or polypropylene may be used. Thefilament extruded through the die 10 is taken up at a given rate by awinder.

The results of mix spinning are shown in Table 4 (Examples 16 to 20).

TABLE 4 Temp. of Extrusion Share Diam. of as spun TLCP EP resin raterate filament Draft strength Example Type of polymer % Type of polymer °C. g/min L/sec μ ratio fs 16 a 50 t 380 250 1.5 × 10⁶ 27 123 5.2 17 a 75n 380 34 2.2 × 10⁵ 35 73 4.8 18 a 25 p 380 41 2.5 × 10⁵ 22 185 5.1 19 c75 n 400 70 4.4 × 10⁵ 51 35 5.0 20 c 25 t 350 36 2.2 × 10⁵ 39 59 3.8TLCP: thermotropic liquid crystal polymer EP: extrudablenon-liquid-crystalline polymer

In Table 4, the types of polymers and the conditions such as the shapeof nozzle are the same as employed in Table 3.

FIGS. 14 and 15 show one mode in which two extruders are employed. Anextruder 111 extrudes a thermotropic liquid crystal polymer while anextruder 112 extrudes an extrudable non-liquid-crystalline polymer. Bothare fed by means of gear pumps 113, 114 into a spun bond die 115. Thetwo resins are separately extruded through respective nozzles 121, 122.As in FIG. 9, a filament 117 having exited the die 115 is passed througha heat insulating mold 62 to reserve heat, drawn through a suction box64, piled on a conveyor belt 47 as a filament assembly 118 and taken uparound a winder 51 as a filament assembly 119 in the form of a nonwovenweb.

Examples 21 to 23

Production of Filament Assembly

Examples 21 to 23 of Table 5 show particular nonwoven webs having highdraft ratios realized by mix spinning.

Experiments were conducted with the use of the melt blow die of FIG. 8.Mix spinning is effective in increasing the draft ratio.

TABLE 5 Temp. of hot air Diam. of TLCP EP resin temp. flow rate filamentDraft as spun Example Type of polymer % Type of polymer ° C. ° C. L/minμ ratio strength 21 a 90 t 380 400 30 16 88 5.1 22 a 90 p 380 400 30 13133 5.4 23 a 75 p 380 400 30 9 278 4.5 TLCP: thermotropic liquid crystalpolymer EP: extrudable non-liquid-crystalline polymer

Examples 24 to 28 and Comparative Example 7

Production of Filament

Examples 24 to 28 of Table 6 show particular nonwoven webs having highdraft ratios realized by mix spinning.

Experiments were conducted with the use of the melt blow die of FIG. 8.While the spinning of TLCP only resulted in a draft ratio of 21(Comparative Example 7), it is easy to attain a draft ratio of 50 orhigher by the spinning of a mixture with EP under the same conditionsand further to attain a draft ratio of 100 or higher by conducting theabove mix spinning with the use of hot air.

TABLE 6 Temp. of hot air Diam. of Example· TLCP EP resin temp. flow ratefilament Draft as spun Comp. Ex. Type of polymer % Type of polymer ° C.° C. L/min μ ratio strength Example 24 a 90 t 380 400 30 13 133 5.5Example 25 a 90 p 380 400 30 11 185 6.1 Example 26 a 75 p 380 400 30 8354 8.2 Example 27 a 75 p 380 — — 17 78 4.1 Example 28 a 75 t 380 — — 2056 3.8 Comp. Ex. 7 a 100 — 380 — — 33 21 2.4 TLCP: thermotropic liquidcrystal polymer EP: extrudable non-liquid-crystalline polymer

The reason why a high draft ratio can be attained by mix spinning of EPand TLCP is as follows. EP and TLCP are mixed together at the stockstage and further kneaded together in the extruder. The shear force inthe nozzle and the draft activity outside the nozzle force the EP towardthe surface of the filament, thereby naturally forming a filamentstructure in which TLCP composes the core while the EP composes thesheath. The presence of the EP at the surface prevents the TLCP fromforming a skin at the surface, thereby realizing a high draft ratio. Inthis connection, the core-forming TLCP has been dissolved away with analkali solution from the filament obtained in Example 12 with the use ofpolypropylene as the EP, and subsequent microscopic observation hasclearly showed the remaining of only the sheath of polypropylene.

In particular, the obtained filament was immersed in a hot aqueoussolution of sodium hydroxide overnight, filtered and washed with water.Subsequent observation by an electron microscope clearly showed thefilament with a hollow structure in which only the sheath remainedundissolved.

That the thus observed filament was nearly completely composed ofpolypropylene was confirmed by a composition analysis. Further, as aresult of separately conducted tests, it has been confirmed that, whileTLCP is readily dissolved in an aqueous alkali solution without leavingany solid, polypropylene is nearly insoluble in the solution to remainas a solid.

In the above process, referring to FIG. 15 showing a view of a lowerside of the spun bond die 115, the separate extrusions of thethermotropic liquid crystal polymer through nozzles 121 indicated bycircles in the figure and the extrudable non-liquid-crystalline polymerthrough nozzles 122 indicated by hatched circles in the figure resultsin the formation of the filament assembly 119 of FIG. 14 which iscomposed of a mixture of two filaments, i.e., those of the thermotropicliquid crystal polymer and the extrudable non-liquid-crystallinepolymer.

A composite (bicomponent or mulchcomponent) filament having acore-sheath structure (or side-by-side structure) can be spun by the useof two extruders. Examples of the composite filaments each having acore-sheath structure are shown in FIG. 16. If this structure is adoptedand if use is made of polypropylene or polyesters exhibiting highsurface draft properties, the formation of a skin of TLCP at the surfacecan be prevented to attain a high draft ratio.

Various types of nozzles for use in the production of synthetic finedenier filaments may be employed in the present invention. As shown inFIG. 17, the inner structure of each filament may be a sectionalstructure like islands being scattered in a sea (FIG. 17A), a splitstructure (FIG. 17B) or a multilayer structure (FIG. 17C), in which thehatched part is formed by extruding the thermotropic liquid crystalpolymer while the other part is formed by extruding the extrudablenon-liquid-crystalline polymer (the polymers may be exchanged). In theconventional process for obtaining fine denier for use in, for example,synthetic leathers, drawing is performed prior to splitting or removalof unneeded resins. With respect to the thermotropic liquid crystalpolymer filament of the present invention, drawing is not needed. It canbe realized that the resins other than the thermotropic liquid crystalpolymer filament may be matrix resins for use in FRP or FRTP or polymerscompatible therewith, the thermotropic liquid crystal polymer beinghighly miscible, from the viewpoint of filament units, with theextrudable non-liquid-crystalline polymer, and that a high shear rate isapplicable to the thermotropic liquid crystal polymer filament.

FIG. 17D shows the filament obtained by the process shown in FIG. 13 forcomparison.

In FIGS. 17B to 17D, the thermotropic liquid crystal polymer componentsconstitute modified cross sections.

In FIG. 18, use is made of an extruder 111 for the thermotropic liquidcrystal polymer and an extruder 112 for the extrudablenon-liquid-crystalline polymer as in FIG. 14. The extruders 111, 112 areprovided with melt blow dies 141, 142, respectively. Separate filaments144, 145 are piled on a conveyor 47 with the use of hot air generated bya hot air generator 143. An assembly 148 composed of a laminate of afilament assembly of thermotropic liquid crystal polymer 156 and afilament assembly of extrudable non-liquid-crystalline polymer 147 istaken up by a winder 51.

FIG. 18 shows a laminate in which each filament assembly forms onelayer. Instead, an increased number of melt blow dies may be disposed sothat thermotropic liquid crystal polymer layers and extrudablenon-liquid-crystalline polymer layers are piled one upon another tothereby improve the productivity and the miscibility.

In FIG. 18, only the melt blow dies are employed. This is not critical,and the spun bond and combination dies may also be utilized.

The inventors formerly proposed nonwoven webs of arranged filaments(Japanese Patent Laid-Open Gazette No. 148861/1989 and U.S. Pat. No.5,312,500).

The inventors found that the extrusion of the molten filament throughthe nozzle 6 and the blowing of hot air (primary hot air) through theapertures 21, 22 provided in close vicinity to the nozzle with the useof the die B or C of FIG. 2 cause the filament 151 in FIG. 19 to vibrate(frequency on the order of 1/100 sec as actually measured by ahigh-speed video camera), and that the application of secondary air152-a, 152-b so as to collide (FIG. 19A) or cross (FIG. 19B) therewitharranges the filaments 153, 154 in the direction X in FIG. 19A and inthe direction Y in FIG. 19B. This principle applies to the thermotropicliquid crystal polymer filament of the present invention. In particular,the thus arranged nonwoven web is highly advantageous because thethermotropic liquid crystal polymer filament can attain high strengthand high elastic modulus without drawing. That is, a product excellentin strength and elastic modulus as a whole body of shaped article can beobtained by the joint application of the effect of the arrangement inthe production of the filament assembly of high strength and highelastic modulus according to the present invention.

The method for vibrating the molten filament 151 is not limited to theabove use of primary hot air and includes the mechanical and electricalmethods described in U.S. Pat. No. 5,312,500.

FIG. 20 is a schematic view of the nonwoven web arranged according tothe present invention, in which the filaments are arranged along thedirection of the arrow. The arrangement of the filaments is not completeas different from the prepreg or the like. It is satisfactory in thepresent invention that, with respect to all the flexed or curledfilaments, 60 to 80% are arranged along a given direction.

FIG. 20A shows one form of filament assembly arranged along onedirection, and FIG. 20B one form of laminate in which the arrangementdirections cross with each other.

Although a vast plurality of nozzles are required for obtaining thearranged filament assembly in the form of a nonwoven web product, in theproduction of a helmet-shaped assembly as shown in FIG. 1, only onenozzle may be used for obtaining a shaped article of a laminate composedof a plurality of layers arranged in arbitrary directions. This can beperformed by changing the direction of disposing the helmet mold alongthe arrangement.

INDUSTRIAL APPLICABILITY

The productivity of the thermotropic liquid crystal polymer filamentaccording to the present invention is high because end breakages do notoccur at the stage of spinning, so that the filament is obtained at alowered cost.

The assembly of thermotropic liquid crystal polymer filaments producedaccording to the present invention has a strength and handlability as awhole of filament assembly because of the entanglement of the filaments.These effects cannot be achieved by the simple assembly of theconventional spun and bundled thermotropic liquid crystal polymerfilaments.

The thermotropic liquid crystal polymer filament composing the filamentassembly of the present invention is a continuous long fiber and hashigh strength and high elastic modulus, thereby ensuring a product ofhigh quality.

The assembly having any desired shape is directly obtained in the stageof spinning. Thus, the process is simplified, so that the cost is lowerthan in the formation thereof from the conventional filaments.

The filament composing the assembly has high strength and high elasticmodulus, which are further improved by heat treatment. Thus, FRP or FRTPof high strength and high elastic modulus can be obtained therefrom. Inparticular, this assembly is composed of a continuous filament, so thatthe properties of the filament are fully utilized effectively. Thisassembly satisfactorily reinforces FRP or FRTP even if the amountthereof is ⅓ to ⅕ of that used when a commercially available filament ischopped and chopped strands are blended with a resin and shaped.

The thermotropic liquid crystal polymer filament of the presentinvention is excellent in elastic modulus and has not only heatresistance but also solvent resistance, high electrical insulatingproperties, dimensional stability attributed to low expansioncoefficient, incombustibility and flame retardancy. Therefore, thethermotropic liquid crystal polymer filament may be formed as it iswithout heat treatment into a filter or a heat insulator.

The filament assembly of the present invention may be used asreinforcing filaments for use in BMC or SMC, as a substitute forasbestos for use in brakes, as a heat insulating material, in a shapedarticle such as a helmet, a container for high-voltage transformer andan automobile bumper and as an independent shaped item such as a filter,a heat insulator, a plate or a pipe.

Further, the filament assembly not only may be used as a heat-resistanthighly strong nonwoven web in the form of a continuous rolled nonwovenweb but also may be integrated with a matrix resin to use as a materialfor sheet molding or stampable sheet.

Still further, the filament assembly may be used in electrical andtransmission parts and in parts for automobiles, marine vessels andaircrafts because of its high electrical insulation, heat resistance andflame retardation.

Still further, the filament assembly may be used as a buffer materialfor holding an object to be heated at the time of induction hardeningand dielectric heating because the induction and dielectric propertiesof the thermotropic liquid crystal polymer filament are excellent.

Mechanical entangling means such as needle punch, stitch bond and waterjet and chemical entangling means with an adhesive may be applied to thefilament assembly of the present invention in order to improve theentanglement of the filaments.

Ceramic adhesives requiring high temperature and time in curing areoccasionally especially suitable because the curing of the ceramic andthe heat treatment of the thermotropic liquid crystal polymer may beconducted simultaneously.

When the filament of a mixture of a thermotropic liquid crystal polymerand an extrudable non-liquid-crystalline polymer according to thepresent invention is incorporated in FTP or FRTP, the quality thereof isexcellent because the thermotropic liquid crystal polymer is highlymiscible with a matrix resin from the viewpoint of filament units andbecause the filament is a long fiber. Further, the product can beproduced at a lowered cost because the cost of the filament assembly islow and because the amount of the thermotropic liquid crystal polymercan be reduced (effect of uniform mixing, effect of long fiber, effectof high molecular orientation in thermotropic liquid crystal polymer,etc.).

With respect to the filament assembly composed of a thermotropic liquidcrystal polymer and an extrudable non-liquid-crystalline polymeraccording to the present invention, the employment of a polymer havingadherence to concrete cement (epoxy resin, vinyl acetate resin, etc.) asthe extrudable non-liquid-crystalline polymer component renders thefilament assembly useful in concrete reinforcement.

FRTP having the filament assembly of thermotropic liquid crystal polymeraccording to the present invention incorporated therein is entirelycomposed of thermoplastic polymers and can be recycled. Therefore, andfurther because it is lightweight and strong, the FRTP would be amaterial most suitable for use in automobile and electrical parts whichare exposed to increasingly strict environmental requirements.

What is claimed is:
 1. A filament assembly comprising a plurality ofmutually entangled long-fiber filaments of a thermotropic liquid crystalpolymer wherein each of the filaments is flexed or curled and has anaverage radius of curvature of 50 mm or less.
 2. The filament assemblyas claimed in claim 1, wherein each of the filaments has a core-sheathstructure in which the non-liquid-crystalline polymer forms the sheathwhile the thermotropic liquid crystal polymer forms the core.
 3. Thefilament assembly as claimed in claim 1, wherein each the tensilestrength of the filaments before heat treatment thereof is at least 2.5g/d.
 4. The filament assembly as claimed in claim 1, wherein eachdiameter of the filaments is 30 um or less.
 5. The filament assembly asclaimed in claim 1, obtained by the process comprising melt spinning athermotropic liquid crystal polymer through a spinning nozzle at a draftratio of at least 30 while holding the filament spun right under thespinning nozzle at a high temperature, wherein the temperature at apoint 50 mm under said nozzle is the melting point of said thermotropicliquid crystal polymer minus 150° C. or higher.
 6. The filament assemblyas claimed in claim 1, wherein the filament assembly can be handled asan integrated body by entanglement of the filaments.
 7. The filamentassembly as claimed in claim 1, wherein each of the filaments consist ofa thermotropic liquid crystal polymer, at least one fibrousreinforcement and at least one additive selected from the groupconsisting of an antioxidant, a heat stabilizer, an ultravioletabsorber, a lubricant, a mold releasing agent, a dye, colorants, a flameretarder, a plasticizer and an antistatic agent.